Hydraulic apparatus



April 26, 1949.

A. c. DARCEY 2,468,489

HYDRAULIC APPARATUS I Filed Dec. 4, 1945 0.05:0 new 65 AyredCDA/ cey.

Patented Apr. 26, 1949 2,468,489 HYDRAULIC APPARATUS Alfred C. DArcey, Norwood, Mass., assignor to Bendix Aviation Corporation, Nor-wood, Mass., a corporation of Delaware Application December 4, 1945, Serial No. 632,681

4 Claims. (Cl. 60-54.5)

The present invention relates to hydraulic apparatus of the character in which the actuating liquid is contained in a closed system; and the motion of a transmitter piston and cylinder assembly is transmitted by the liquid to a receiver piston and cylinder assembly.

While apparatus of this general character have gone into comparatively wide use, they are open to the objection that the liquid expands and contracts in response to temperature changes, with the result that the receiver piston and cylinder assembly will not accurately follow the motion of the transmitter piston and cylinder assembly. In hydraulic apparatus of the character in which dual transmitter and receiver fluid motor assemblies are employed, for producing positive bi-directional actuation, it is necessary to employ a closed system. This entails bleeding ofi a portion of the liquid when the temperature rises, to prevent rupture of the lines. In that type of system, the thermal compensating operation is extremely inconvenient because any fluid bled off during fluid expansion must be returned to the system upon contraction of the fluid. Otherwise there would be a free air space which would introduce an undesirable yield or lost motion into its operation.

Although it has been heretofore proposed to compensate for temperature changes in systems of this general character by allowing the expanding fluid to bleed oil into bellows devices, and so called Choke Coils have been employed in an efiort to control flow of the fluid, and prevent it from responding to the momentary pressures which develop incident to normal operation of the system, such attempts have not proven altogether successful; esepecially since no provision has been made to maintain a pressure in the device at all times which would insure return of fluid to the system upon contraction of the liquid, and which would equalize the pressure in both directions.

It is the primary object of this invention to provide a novel hydraulic apparatus which is fully closed, which will cause the receiver piston to accurately follow the transmitter piston irrespective of temperature changes, will allow fluid to bleed from the apparatus when the temperature rises, will promptly return fluid to the apparatus when the temperature falls, and yet which will not subject any of the hydraulic lines to pressures which would rupture them or produce mechanical failure of any of the parts of the units.

Another important object is to provide hydraulic apparatus of the dual fluid motor type,

with a novel thermal compensating assembly.

which will place each of the fluid lines under a predetermined hydrostatic pressure when the system is at rest, which will allow free ingress of fluid into, and free egress of fluid from the lines in response to temperature changes, and yet afiord an assembly in which the predetermined hydrostatic pressure wil cause the receiver motors to accurately follow movement of the transmitter motors, without yield or lost- ,motion. Another object is to provide, for use in a hydraulic apparatus of the dual fluid actuator type, a novel thermal compensation unit adapted to be placed in fluid communication with the hydraulic lines and which is so designed that it will not set up resistance to flow of fluid through the lines, and yet will accurately compensate for temperature changes of the hydraulic fluid and will cause the receiver member to accurately follow its transmitter member, without yield or lostmotion.

A further object is to provide a novel hydraulic apparatus embodying dual hydraulic lines and a unit for placing the fluid in the lines under a predetermined adjustable hydraulic pressure at all times and which will permit expanding fluid to escape from the lines in response to increase in temperature and yet will exert suflicient resistance to fluid flow during actuation as to cause the receiver member to accurately reproduce the motion of the transmitter member.

Further objects will become apparent as the specification proceeds in conjunction with the annexed drawings, and from the appended claims. I

In the drawings: i

Fig. 1 is a side elevational view, with parts in section, of a hydraulic system embodying the invention, and

Fig. '2 is a longitudinal vertical sectional view, on an enlarged scale, through the compensator unit shown in Fig. 1.

With continued reference to the drawings, in which like reference characters have been employed to designate similar parts thoughout the several views, I have illustrated the invention as being applied to a so-called remotely controlled or actuated assembly embodying an actuator or transmitter unit I l and an actuated or receiver unit l2, although it is understood that the invention is not limited thereto and may be used with other types of hydraulic units, if desired. It is also to be understood that the in- 3 vention is not limited to use with transmitter and receiver units of the piston and cylinder type, inasmuch as it may be successfully utilized with those embodying diaphragms and the like.

The transmitter unit comprises a pedestal l3 upon which an actuating lever I4 is journalled for rocking movement between the closed and opened positions indicated. Rigidly secured to lever|4 is a rocker arm l5. Pivotally connected to the ends of the rocker arm, by means of pins l6 and I1, are piston or connecting rods I8 and I9 respectively. A pair of pistons 2| and 22 are connected to the piston rods by wrist pins in well known manner and reciprocate in cylinders 23 and 24 respectively formed in the bottom of a hydraulic fluid reservoir 25. Fluid may be introduced into the reservoir by way of a passage 26 formed in the pedestal and closed by a vent cap 21. The latter prevents dust and extraneous material from entering the reservoir and yet permits free ingress and egress of air in response to thermal expansion of the fluid. As seen in Fig. 1, the reservoir is filled with fluid approximately to the level indicated by the reference character 28, so that the pistons are submerged at all times, and yet when the expansion of the fluid occurs in response to temperature changes there is sufflcient expansion space to prevent it from escaping through the filler opening.

Cylinders 23 and 24 are connected by lines 29 and 3| respectively to a pair of cylinders 32 and 33 formed in the bottom of receiver unit l2. The latter also provides a fluid reservoir 34 in which a body of'fluid 35 may be maintained to keep its pistons 36 and 31 submerged at all times, A detachable closure 38 is secured to unit l2 by screws 33 in well known manner, and a filler port may be provided of similar construction to the one discussed in conjunction with the transmitter unit, as is well understood in the art. It has been omitted to simplify the disclosure.

A pair of connecting rods 4| and 42 are pivotally connected to pistons 36 and 31 in well known manner and they are pivotally connected at their upper ends to a rocker arm 43. The latter is rigidly clamped 'to a shaft 44 journalled in the walls of reservoir 34.

Adjustably but rigidly secured to shaft 44, exteriorly of the casing, by means of a clamp screw 45 is a lever 46, which, in the particular application of the invention disclosed, is the actuated member. Lever 48 is provided with a plurality of openings 41. Pivotally secured in one of the openings is a swivel unit 48 having a link 49 rigidly secured thereto. The other end of the link is pivotally connected to an arm 5| by means of a swivel unit 52. Arm 5| is carried by a shaft 53, which may constitute the throttle shaft of a carburetor or any other device which it is desired to actuate, adjustment of the idle position of arm 5| being provided by a screw 54 adjustably threaded into a bracket 55 or any other suitable stationary part of the device and coacting with the arm.

The structure so far described constitutes a I conventional remote controller for a throttle or the like, and it is apparent that upon swinging actuator lever l4 clockwise through approximately 90 into theindicated open position, piston 22 will be forced downwardly in cylinder 24, which in turn forces liquid through line- 3| into cylinder 33. This in turn causes piston 31 to lift and rock shaft 42 and arm 46 clockwise through approximately 90 into the open throttl position, thereby through link 49 causing arm 5| to assume a similar position. During the opera= tion just described, piston 36 is forced downwardly in its cylinder 32, thereby causing fluid to pass through line 29 and into cylinder 23, in conta ct with its retreating piston 2|.

I have found that by providing the system just described with a resiliently actuated expansible chamber assembly, and so designing it as to place lines 29 and 3| under equalized pressures of substantial magnitude when the unit is at rest, and properly restricting the flow of fluid to and from the lines, it is possible to maintain lines 29 and 3| totally closed as shown and yet achieve a system which will automatically compensate for all temperature changes, and at the same time will cause the actuated member to accurately follow the actuating member. This is accomplished by the novel structure which will now be described.

The thermal compensator takes the form of sectional or duplicate cylinder unit 51 which may be supported in any well known manner adjacent either the transmitter or the receiver unit, or at some intermediate location, depending upon the installation conditions at hand, for convenient connection to the lnes 29 and 3|.

As seen more clearly in Fig. 2, the unitis made up of a pair of open-ended, flanged cylinder members 58 and 59, having their flanges secured together by a plurality of bolt and nut assemblies 6|. A spacer 62 is clamped between the cylinder members and is provided with a plurality of vents 63, which provide free atmospheric communication to the interior of the bellows units, which will now be described. Rigidly secured in sealing relationship to the walls of cylinders 58 and 59 are flanged washers 64 and 65 respectively, which are in turn secured to bellows units 66 and 51, The outer ends of the bellows are closed by discs 68 and 69, against which the opposite ends of a compression spring -1| bear. The spring is centered in any suitable manner, as by means of lugs 12 and 13 secured to discs 68 and 69.

From the structure so far developed it is apparent that the outer walls of the bellows cooperate with cylinders 58 and 59 to provide closed chambers, the pressures in such chambers being equal to each other and proportional in magni tude to the force exerted by spring 1|. Any air in the chamber during filling may be vented by individual venting assemblies made up of a sleeve 14 secured to the cylinder and threadedly carrying a valve 15 which cooperates with an opening 16 in the cylinder. When the valve is backed off, air may escape through cylinder opening 16 and through a vent hole 11 provided in the sleeve 14. Since the venting assemblies are identical, only one of them has been described in detail.

The interior of cylinders 58 and 59 are placed in fluid communication with lines 3| and 29 respectively by means of lines 18 and 19,it being particularly observed that lines 18 and 19 are of comparatively small diameter and are provided with extensions 8| and 82 which extend near to the bottoms of their respective cylinders so as to prevent the entry of air. Extensions 8| and 82,

for convenience of assembly, may be madesepa- .rately from lines 18 and 19 if desired.

by cap screws 89 and 9|.

From the structure so far described it is apparent that with the system at rest, compression spring II, in acting upon one bellows and reacting against the other bellows, will set up equal pressures in cylinders 58 and 59, and these pressures will be transmitted by lines 18 and 19 to lines 3| and 29 respectively. It is also apparent that these equalized pressures will not produce actuation of either the transmitter or receiver pistons.

Assuming now that the temperature of the fluid increases, causing an expansion of the fluid in lines 29 and 3|, it is apparent that the excess may freely expand through lines 18 and 19 into cylinders 58 and 59 against the yielding pressure of spring 1 I. Conversely, when the temperature drops, spring II will force the liquid out of cylinders 58 and 59 back into lines 29 and 3|. The foregoing highly desirable bleeding action is secured by making lines 18 and 19 of somewhat restricted diameter, or of so-called capillary size, so that when actuating handle I4 is operated there will be no substantial transfer of energy between lines 29 and 3| by way of spring H and bellows 56 and 61. In other words, the compensator will respond to sustained pressures, such as those produced by thermal expansion of the fluid, but it will not substantially respond to suddenly applied pressures, such as those set up in response to operation of the actuating handle.

It should be particularly observed that spring 1| may be adjusted to produce the desired pressure by screws 85 and 86. The procedure is as follows:

At the time of initially filling the system with liquid screws 89 and 9| are removed and a screwdriver is utilized to thread screws 85 and 86 into engagement with their seats 8'! and 88. After contact is made, further movement of the screws causes the bellows to undergo contraction, and this also causes pressure to build up in compression spring II. It is apparent that the greater the pressure built up in the spring the greater will be the hydraulic pressure subsequently developed by the bellows. Assuming now that screws 85 and 86 have been adjusted so as to place spring II under the desired degree of compression, the bellows chambers are then filled with liquid, any air present being bled by opening valves 15. When the system is full, screws 95 and 86 are then backed off into the full-line positions of Fig. 2 and screws 89 and 9| are replaced. The device is now ready for operation. In the event that after the device has been placed in operation it is found that the pressure is too high, it may be reduced the desired amount by opening bleed valves and allowin a predetermined quantity of liquid to flow from each valve. The-same amount is bled from each end of the device so as to maintain the bellows and spring assembly properly centered with respect to the casing.

It should be particularly observed that spring H performs two highly important functions. First, it insures prompt return of fluid to the system in response to a drop in temperature, under the controlling influence of flow restricting lines 18, 19, BI and 82, so that the system is always full of fluid and there are no air spacers which would cause a yield or lost-motion between the transmitter and receiver units. Secondly, spring II sets up a pressure of substantial magnitude,

of lines 18, 19, 8| and 82, prevents any substantial transfer of energy between lines 29 and 3| by way of spring II and bellows 56 and 91. In other words, actuation of lever I 4 in one direc tion normally causes an increase in pressure in one of lines 29 and 3| and a pressure drop in the other, and by placing them both under substantial pressure by spring N, there is much less tendency for transfer of energy by way of the spring and consequent yield of the transmitter unit with respect to the receiver unit.

- From the foregoing detailed disclosure it is apparent that the invention provides a hydraulic system which is automatically compensated for thermal expansion and contraction of the fluid and that while the automatic expansion chambers are operable toreceive liquid from the sysso that when handle II is actuated in either y tem when the liquid expands in response to a temperature rise, the device will not permit such flow of liquid from the system, in response to a suddenly applied pressure, such as for instance is produced by actuation of the transmitter unit in the normal operation of the system, and yet the device exerts a constant, resiliently-generated fluid pressure which is suflicient to cause it to return liquid to the system in the event the temperature thereof decreases, and also suflicient to prevent any substantial transfer of energy between lines 29 and 3| by way of spring 1|, thereby obviating the possibility of drawin air into the system, and at the same time precluding the introduction of lost-motion or yield into the operation.

It is to be understood that the foregoing detailed disclosure of the preferred embodiment of the invention is given by way of illustration of the best physical form of the invention now known, and that other forms of the invention, within the range of equivalents, are intended to be embraced by the appended claims.

What is claimed and desired to be secured :by Letters Patent of the United States is:

1. In a hydraulic apparatus of the character having a pair of fluid pressure lines which are operably associated with transmitter and receiver units, a device for compensating for thermal expansion and contraction of fluid in said lines, comprising a pair of expansible chamber assemblies having means placing one of the assemblies in fluid communication with one of said fluid pressure lines and the other assembly in fluid communication with the other fluid pressure line, said expansible chamber devices each having a movable wall, spring means acting against one of said walls and reacting against the other wall in such manner as tocause their associated chambers to tend to force fluid into said fluid pressure lines under pressures of substantially equal magnitude; and conditioning means for forcing said movable walls in a pressure relieving direction against the action of said spring means at will independently of the pressure in said fluid pressure lines, for the purpose of introducing a predetermined quantity of fluid into said expansible chamber devices, and building up a force of predetermined magnitude in said spring means.

2. The apparatus defined in claim 1, wherein said conditioning means comprises a mechanical device operably associated with each of said movable walls and operable to force the latter in pressure relieving directions independently. of each other, whereby the quantity of fluid introduced into each of said expansible chamber devices may accurately be predetermined.

3. In a remote controlled hydraulic apparatus of the dual unit type, inwhich mating pairs of transmitter and receiver units are hydraulically connected by a pair of fluid lines and the pairs of transmitter and receiver units are mechanical- 1y interconnected so that bi-directional movement of the transmitter units efiects bi-directional actuation of the receiver units; and means, hydraulically co-acting with said fluid lines, for causing said apparatus to automatically compensate for thermally induced expansion and contraction of the hydraulic fluid, comprising a pair of variable volume chambers each having a movable wall, means placing one of said chambers in fluid communication with one of said hydraulic lines and the other chamber in fluid communication with said other hydraulic line, resilient means co-acting with said movable walls and constantly tending to reduce the volume of said chambers, and means for selectively increasing the volume of said chambers against the action of said resilient means, to thereby adjustably 'vary the force built up in the latter and the fluid pressure in said hydraulic lines.

4. The hydraulic apparatus defined in claim 3, wherein a pair of conduits interconnect said pair of chambers with said hydraulic lines, one of said REFERENCES CITED 7 The following references are of record in the file of this patent:

UNITED STATES PATENTS 20 Number Name Date 375,674 Greene Dec. 27, 1887 1,862,569 Gargan June 14, 1932 FOREIGN PATENTS 25 Number Country Date 776,645 France Nov. 8, 1945 377,433 Italy Dec. 16, 1939 

